1. Field of the Invention
This invention relates to an illumination apparatus and a liquid crystal display apparatus, and more particularly to an illumination apparatus for allowing light from a light source to be planarly emitted by a light guide plate and to a liquid crystal display apparatus of the pseudo-impulse type equipped with this illumination apparatus.
2. Background Art
Recently, liquid crystal display apparatuses (hereinafter also referred to as “LCDs”) have been rapidly prevailing as thin display apparatuses. However, in comparison with CRT (cathode-ray tube) display apparatuses (hereinafter simply referred to as “CRTs”), LCDs suffer from blur of moving images and low contrast. That is, in CRTs, between the emission period of a pixel in a frame and the emission period of this pixel in the next frame, there is a non-emission period in which this pixel does not emit light, hence producing little afterimage. On the other hand, the display method of LCDs is of the “hold type” lacking such non-emission period. Hence afterimage occurs, and is perceived as blur of moving images by users. Furthermore, CRTs have high contrast because pixels do not emit light during black display. On the other hand, when an LCD displays black, the liquid crystal panel is turned into a light shielding state while the light source keeps emitting light. However, it is difficult to completely shield light even if the liquid crystal panel is turned into the light shielding state. Thus LCDs have low contrast.
To eliminate afterimage in LCDs, it is effective to insert a non-emission period for black display between one emission period and the next emission period for image display as in CRTs to provide a “pseudo-impulse type” display method. This can be realized by providing an emission period for image display and a non-emission period for black display within one frame. However, when a moving image is displayed at 60 Hz, one frame has a time span of 16.7 ms (milliseconds), whereas liquid crystal typically has a response time of 10 ms or more. Hence it is difficult to realize two displays, i.e., image display and black display, within one frame by controlling liquid crystal.
To solve this problem, in a proposed technique for a backlight type LCD using cold-cathode tubes as a light source, black display is inserted between image displays by successively turning out the cold-cathode tubes in synchronization with the timing of applying a video signal to the liquid crystal panel. Thus it is possible to realize pseudo-impulse type display, thereby preventing afterimage, enhancing contrast, and reducing power consumption.
On the other hand, small LCDs are often based on sidelight type LCDs for reducing thickness, where light from a light source is planarly emitted by a light guide plate. It is desirable to apply the above pseudo-impulse type display method also to such sidelight type LCDs. For example, in a technique proposed in JP 2001-210122A, a light guide plate is composed of a plurality of blocks, which are optically separated by reflection plates placed between the blocks, and a white LED (light emitting diode) is provided for each block. While a block emits light, other blocks adjacent to this block do not emit light. Thus pseudo-impulse type display can be realized.
Unfortunately, the technique disclosed in JP 2001-210122A needs work for providing reflection plates in the light guide plate, which increases cost. Furthermore, the reflection plates absorb light, and hence decreases the utilization efficiency of light.